Plastic batteries of the present invention are electrolytic cells comprising polymeric composition electrode and electrolyte members, and are described for example in prior U.S. Pat. Nos. 5,196,279 and 5,296,318 both of which are incorporated by reference in their entirety. The development of plastic batteries has improved the properties of rechargeable batteries and has expanded the applications for which batteries can function effectively.
Relatively small plastic batteries possess large surface areas and have only limited energy and therefore cell overheating is quite unlikely, even in the event of a short circuit. This is in contrast to similarly small sized liquid lithium ion batteries which normally require a safety mechanism, generally in the form of a positive temperature coefficient ("PTC") switch which places the cell into an open-circuit condition when the cell temperature exceeds a predetermined temperature, usually in the range of 100.degree. C. An example of a PTC resistor for a liquid lithium ion battery is described in U.S. Pat. No. 5,376,467. Larger plastic batteries, especially those having powers greater than 100 Wh may exhibit cell overheating similar to that experienced in liquid lithium ion batteries and therefore require safety features which act to open the battery circuit in the event of cell overheating or in the event of local short-circuit.